http://www.marxists.org/archive/marx/works/1885-c2/ch06.htm
We are concerned here only with the general character of the costs of circulation, which arise out of the metamorphosis of forms alone. It is superfluous to discuss here all their forms in detail. But how forms which belong in the sphere of pure changes of the form of value and hence originate from the particular social form of the process of production, forms which in the case of the individual commodity-producer are only transient, barely perceptible elements, run alongside his productive functions or become intertwined with them — how these can strike the eye as the huge costs of circulation can be seen from just the money taken in and paid out when these operations have become independent and concentrated on a large scale as the exclusive function of banks, etc., or of cashiers in individual businesses. But it must be firmly borne in mind that these costs of circulation are not changed in character by their change in appearance.
This is in volume 3:
http://www.marxists.org/archive/marx/works/1894-c3/ch25.htm
The other side of the credit system is connected with the development of money-dealing, which, of course, keeps step under capitalist production with the development of dealing in commodity. We have seen in the preceding part (Chap. XIX) how the care of the reserve funds of businessmen, the technical operations of receiving and disbursing money, of international payments, and thus of the bullion trade, are concentrated in the hands of the money-dealers. The other side of the credit system — the management of interest-bearing capital, or money-capital, develops alongside this money-dealing as a special function of the money-dealers. Borrowing and lending money becomes their particular business. They act as middlemen between the actual lender and the borrower of money-capital. Generally speaking, this aspect of the banking business consists of concentrating large amounts of the loanable money-capital in the bankers' hands, so that, in place of the individual money-lender, the bankers confront the industrial capitalists and commercial capitalists as representatives of all moneylenders. They become the general managers of money-capital. On the other hand by borrowing for the entire world of commerce, they concentrate all the borrowers vis-à-vis all the lenders. A bank represents a centralisation of money-capital, of the lenders, on the one hand, and on the other a centralisation of the borrowers. Its profit is generally made by borrowing at a lower rate of interest than it receives in loaning.
The loanable capital which the banks have at their disposal streams to them in various ways. In the first place, being the cashiers of the industrial capitalists, all the money-capital which every producer and merchant must have as a reserve fund, or receives in payment, is concentrated in their hands. These funds are thus converted into loanable money-capital. In this way, the reserve fund of the commercial world, because it is concentrated in a common treasury, is reduced to its necessary minimum, and a portion of the money-capital which would otherwise have to lie slumbering as a reserve fund, is loaned out and serves as interest-bearing capital. In the second place, the loanable capital of the banks is formed by the deposits of money-capitalists who entrust them with the business of loaning them out. Furthermore, with the development of the banking system, and particularly as soon as banks came to pay interest on deposits, money savings and the temporarily idle money of all classes were deposited with them. Small amounts, each in itself incapable of acting in the capacity of money-capital, merge together into large masses and thus form a money power. This aggregation of small amounts must be distinguished as a specific function of the banking system from its go-between activities between the money-capitalists proper and the borrowers. In the final analysis, the revenues, which are usually but gradually consumed, are also deposited with the banks.
JH: And so on and so forth.
Note the following passage above: " In this way, the reserve fund of the commercial world, because it is concentrated in a common treasury, is reduced to its necessary minimum, and a portion of the money-capital which would otherwise have to lie slumbering as a reserve fund, is loaned out and serves as interest-bearing capital."
The mere expansion of FIRE does not mean "hypertrophy" of circulation costs or undue lengthening of circulation time globally considered. For capital as a whole, part of this expansion is actually a net reduction in circulation costs and circulation time.